Weather MCP Server

Instructions

Implementation Reference

• src/weather/server.py:17-34 (handler)

  The main handler function for the 'get_alerts' tool. It is registered via the @mcp.tool() decorator. Fetches active weather alerts for a US state from the NWS API, formats them using helpers, and returns a formatted string.

  @mcp.tool()
  async def get_alerts(state: str) -> str:
      """Get weather alerts for a US state.
  
      Args:
          state: Two-letter US state code (e.g. CA, NY)
      """
      url = f"{NWS_API_BASE}/alerts/active/area/{state}"
      data = await make_nws_request(url)
  
      if not data or "features" not in data:
          return "Unable to fetch alerts or no alerts found."
  
      if not data["features"]:
          return "No active alerts for this state."
  
      alerts = [format_alert(feature) for feature in data["features"]]
      return "\n---\n".join(alerts)

• src/weather/server.py:19-23 (schema)

  Input schema for the tool defined in the docstring: expects a 'state' parameter as a two-letter US state code.

  """Get weather alerts for a US state.
  
  Args:
      state: Two-letter US state code (e.g. CA, NY)
  """

• src/weather/server.py:75-88 (helper)

  Helper function used by get_alerts to make authenticated HTTP requests to the National Weather Service API.

  async def make_nws_request(url: str) -> dict[str, Any] | None:
      """Make a request to the NWS API with proper error handling."""
      headers = {
          "User-Agent": USER_AGENT,
          "Accept": "application/geo+json",
      }
      async with httpx.AsyncClient(follow_redirects=True) as client:
          try:
              response = await client.get(url, headers=headers, timeout=30.0)
              response.raise_for_status()
              return response.json()
          except Exception:
              return None

• src/weather/server.py:90-100 (helper)

  Helper function used by get_alerts to format individual alert features into readable text.

  def format_alert(feature: dict) -> str:
      """Format an alert feature into a readable string."""
      props = feature["properties"]
      return f"""
  Event: {props.get('event', 'Unknown')}
  Area: {props.get('areaDesc', 'Unknown')}
  Severity: {props.get('severity', 'Unknown')}
  Description: {props.get('description', 'No description available')}
  Instructions: {props.get('instruction', 'No specific instructions provided')}
  """